<p>An improved block-based model (BBM) combined with Voronoi tessellation to consider the particle outline and mineral composition is proposed to investigate the mechanical and microscopic fracture behavior of calcareous nodules. First, the single-particle crushing tests were conducted on calcareous nodules to investigate the macro mechanical properties. Then, the procedure to build a 3D BBM by incorporating polyhedral cells into the discrete element method (DEM) was introduced, and a sensitivity analysis on cell size was discussed as a part of preparation for reconstructing the calcareous nodule model. Microparameter calibration was performed to match the macro failure strength observed in experiments. It is shown that crack types are mainly tension cracks that are parallel or subparallel to the loading direction during the whole loading. The load-induced microcracks mainly appear at particle boundaries, followed by the intra-granular microcracks including calcite, quartz, and albite. Mineral morphology has a clear effect on the failure strength, that is, higher values of cell sphericity result in a larger failure strength. This study provides an effective method for simulating single-particle breakage of calcareous nodules in the BBM. </p>